Angle sensor with reduction gear

ABSTRACT

In a flat housing (10) a stator (12) is concentrically arranged relative to an input shaft (16) supported in the housing (10). A rotor (14) is seated on the input shaft (16). A reducing gear (18) constructed as a play-free planetary gear is arranged within the flat housing (10) in an annular space (20) formed between the rotor (14) and the input shaft (16). The signal processing circuit is also accommodated in an annular space (60) within the housing (10). The input shaft (16) can be rotated through 360° or more. During such rotation, the rotor (14) performs a rotational movement through a limited angle within which there is obtained a substantially linear angle signal due to the cooperation of the rotor (14) and the stator (12).

TECHNICAL FIELD

The invention relates to an angle transmitter containing

(a) a flat housing,

(b) a stator arranged in the flat housing,

(c) a rotor rotatably supported relative to the stator in the housingand cooperating with the stator through a limited angular range forproducing an output signal dependent upon the rotational angle,

(d) an input shaft and

(e) a reducing gear by means of which the input shaft is coupled to therotor.

BACKGROUND ART

German Patent Publication No. 3,212,149 describes an angle transmitterin which the stator contains a coil wound along a circular arc andcontaining a central tap. The coil is seated upon an annular core madeof non-magnetic material and having substantially rectangularcross-section. Strips of magnetic material are inserted into theinterior surface and into the exterior surface of the annular core. Thisstator is seated in a flat box-shaped housing. The rotor is journalledin the housing by means of a shaft. The rotor is constructed as a rotarymember containing a disc and two coaxial ribs extending along thecircumference of the disc. The ribs extend internally and externallyaround the coil. The rotor is manufactured from non-magnetic material.Strips of ferromagnetic material are sunk into the outer side of theinner rib, into the inner side of the outer rib, which sides face thecoil. These strips extend over part of the circumference. Theferromagnetic strips affect the stray field and effect a change in theinductances of the coil portions on both sides of the central tap whenthe rotor is rotated. A circuit arrangement responds to these changesfor generating an angle signal. In the known angle transmitter the rotorcan be rotated through full circle. However, an angle signal which isproportional to the rotational angle, can be obtained only through alimited angular range of, for example, 90°.

For this reason the known angle transmitter has been provided with areducing gear. An input shaft is coupled to the rotor via such reducinggear. Therein the input shaft jointly with the reducing gear is seatedin a separate housing which is attached to the recited flat housingaccording to German Patent Publication No. 3,212,149. The output shaftof this gear is coupled to the shaft which carries the rotor. The inputshaft, then, can be rotated through 360° or, if required, even through agreater angle, whereas the rotor moves within the range in which alinear angle signal is obtained. The circuit arrangement which respondsto changes in the inductances of the two coil portions for generatingthe angle signal is also accommodated in a separate housing, which isattached to the flat housing of the actual angle transmitter in apractically realized known arrangement of the type according to GermanPatent Publication No. 3,212,149.

Thus, for the overall arrangement, there result relatively great axialdimensions which are undesired for many uses.

The same problem also occurs in angle transmitters operating accordingto a different principle, for example, in angle transmitters in which anarmature which contains a core of low-retentivity material, more or lesswidely extends into arcuately wound coil portions and the core is movedfarther into the one coil half and correspondingly farther out from theother coil half when the armature is rotatably moved out from a centralposition.

German Patent Publication No. 3,325,318 describes an incremental angleencoder containing means for optional adjustment of an absolute zeropoint or reference point. These means consist of a reducing gear whichis coupled to the angle encoder shaft on the drive side and on thedriven side to a disc comprising an opto-electronically scannable boreor light reflection mark. The disc constitutes a gear wheel which iscoupled to the reducing gear by means of a sliding clutch and which canbe externally adjusted using a tooth wrench provided with a pinion. Theabsolute zero point thereby can be adjusted for the incremental angletransmitter.

In this arrangement the disc of the angle encoder, the reducing gearwhich is constructed as a planetary gear, and the gear wheel are axiallyseries arranged. Thus there results an undesirably great overall lengthwhich is a bar to the accommodation in a flat housing.

German Patent Publication No. 2,659,760 shows an arrangement forindicating the angular position of a rotatable member provided with ashaft, for example, the printing head of an office machine. Therein therotary movement of the shaft which constitutes the input shaft of thearrangement is transmitted to a second shaft by means of a gear wheeltransmission in a speed changing manner. A drum containing aphotoelectrically operating incremental angle encoder is seated on thesecond shaft. In this manner only a partial revolution of the inputshaft corresponds to a complete revolution of the drum in correspondencewith the transmission ratio. Therefore, small angle increments of theinput shaft are covered by relatively coarse angle increments of thedrum. In order to obtain a zero point which corresponds to apredetermined position of the input shaft, a second drum is arrangedwithin the drum. The second drum is rotatably journalled at the secondshaft and coupled thereto via a reducing gear arranged within theinterior of the second drum. The reduction is selected such that thesecond drum is rotated through the same angle as the input shaft. Thesecond drum is also photoelectrically scanned and supplies the zeropoint.

Both the arrangements according to German Patent Publication Nos.3,325,318 and 2,659,760 constitute incremental angle transmitters whichare driven through a number of revolutions either directly as accordingto German Patent Publication No. 3,325,318 or via a speed changingtransmission as according to German Patent Publication No. 2,659,760.The members driven via a reducing gear do not constitute angletransmitters but only supply a zero point. These arrangements are notconcerned with an angle transmitter containing a rotor which cooperateswith a stator through a limited angular range for generating an outputsignal dependent on the rotational angle, and with the accommodation ofsuch angle transmitter, together with the reducing gear in a flathousing.

DISCLOSURE OF INVENTION

The invention is based on the object of constructing an angletransmitter of the initially mentioned type such that its axialdimensions become the smallest possible dimensions.

In accordance with the invention this object is achieved in that

(f) the input shaft is journalled in said flat housing,

(g) the rotor is rotatably supported at the input shaft and

(h) the reducing gear is arranged within the flat housing in an annularspace formed between the rotor and the input shaft.

In this manner a space utilized for receiving the reducing gear which ispresent in the flat housing, in any case. It is not required that stillfurther housing including an input shaft and reducing gear be attachedto the flat housing.

In contrast to the described known arrangement the input shaft which isrotatable through at least 360° and coupled to the rotor via thereducing gear, is journalled as such in the recited flat housing and nota shaft which is rigidly coupled to the rotor and practically rotatedonly through a limited angle. Contrary to German Patent Publication No.3,212,149 the rotor is not rigidly coupled to a shaft but rotatablysupported at the input shaft. The reducing gear is not seated in aseparate housing, but within the flat housing which also contains thestator and the rotor. There results thus a highly space-saving angletransmitter having small axial dimensions.

Constructional realizations of the invention are the subjects of thedependent claims.

BRIEF DESCRIPTION OF DRAWINGS

In the following, an exemplary embodiment of the invention is explainedin more detail with reference to the associated drawings:

FIG. 1 shows in a broken-off manner a section through an angletransmitter of the instant type.

FIG. 2 is a schematic top plan view of the angle transmitter.

FIG. 3 shows the related circuit diagram.

PREFERRED MODES FOR CARRYING OUT THE INVENTION

The angle transmitter contains a flat housing 10. A stator 12 isarranged in the flat housing 10. Furthermore, a rotor 14 is rotatablysupported relative to the stator 12 in the housing 10. The rotor 14cooperates with the stator 12 through a limited angular range forgenerating an output signal which is dependent upon the rotationalangle. An input shaft 16 is coupled to the rotor 14 via a reducing gear18.

The input shaft 16 is journalled in the recited flat housing 10. Therotor 14 is rotatably supported at the input shaft 16. The reducing gear18 is arranged within the flat housing 10 in an annular space 20 formedbetween the rotor 14 and the input shaft 16. The reducing gear 18contains an external toothing 22 at the input shaft 16 as well as aninternal toothing 24 at the rotor 14 concentric relative to the inputshaft 16 and gear means 26 spaced therefrom and rotatably journalled inthe housing 10 and which gear means 26 mesh with the external housing 22of the input shaft 16, on the one hand, and with the internal toothing24 of the rotor 14, on the other hand.

For play-free transmission of the rotary movement, the gear means 26comprises a first gear wheel 28 and a second gear wheel 30 similarthereto and which gear wheels are rotatably supported at an axle 32fixed relative to the housing. The first and second gear wheels 28 and30 are interconnected by (FIG. 1) elastic members such that their teethare slightly angularly offset from each other in an idle position. Thegear wheels, then, can be engaged with the external toothing 22 of theinput shaft 16 and with biasing of the elastic members such that theflank of one tooth of the first gear wheel 22 resiliently engages arelated tooth of the external toothing 22 and the opposite flank of thecorresponding tooth of the second 30 is resiliently engaged with theadjacent tooth of the external toothing 22. In this manner thetransmission of the rotational movement of the input shaft 16 to thefirst and second gear wheels 28 and 30 is effected free of play. Thegear means 26 further contain a third gear wheel 34 which is alsorotatably supported at the axle 32 which is fixed relative to thehousing. The third gear wheel 34 is free from the external toothing 22of the input shaft 16 and thus in engagement with this external toothing22. The third gear wheel 34 is connected with the adjacent second gearwheel 30 by means of elastic members 36 such that their teeth areslightly angularly offset from each other in an idle position. Thesecond and third gear wheels 32 and 34 mesh with the internal toothing24 of the rotor 14 and freedom from play is generated again in thedescribed manner by biassing the elastic members 36.

The rotor 14 contains a hub 38 which is rotatably supported at the inputshaft 16 adjacent the external toothing 22 of the input shaft 16 bymeans of two rolling bearings 40 and 42. An annular disc-shaped centralportion 44 adjoins the hub 38. of the hub 38, which end is adjacent theexternal toothing 22 and thus at the lower end of the hub 38 in FIG. 1.The central portion 44 is followed along its circumference and on theside remote from the hub 38, by a circumferential portion 46 having abasic cylindrical shape. The internal toothing 24 is provided at thiscircumferential portion 46 on the inside thereof. The gear means 26protrude into the annular space 20 bounded by the circumferentialportion 46, the central portion 44 and the input shaft 16.

The input shaft 16 is journalled in rolling bearings 48 and 50 providedin related cover members 52 and 54 of the housing 10. The cover member52 therein comprises a collar 66 in which the bearing 48 is seated. Thecover member 54 comprises along its outer rim a collar 58 at which thestator 12 is retained. The axle 32 is also seated in the cover member54. The hub 38 of the rotor 14 and the external toothing 22 of the inputshaft 16 are arranged at the input shaft 16 between the rolling bearings48 and 50. A further annular space 60 is formed around the hub 38between the central portion 44 of the rotor 14 and the cover member 52of the housing 10. Signal processing electronic components of a circuitarrangement delivering the angle signal are arranged at an annularprinted circuit board 62 within this annular space 60. The housing 10 isprovided with a magnetic shield 64 made of mu-metal.

In this manner not only the gear 18 is accommodated by the flat housing10. The housing 10 also contains the components of the signal processingcircuit.

In the illustrated embodiment the stator 12 comprises a coil 66 which iswound along a circular arc and contains a central tap 67 and coil ends67a, 67b and an at least partially ferromagnetic core 68. The rotor 14comprises an at least partially ferromagnetic armature which internallyextends around the coil 66 in a manner such that only the stray field isaffected. There is provided a circuit arrangement which includescomponents mounted at the printed circuit board 62 and also responds tochanges in the inductances of the coil members formed on both sides ofthe central tap, for generating an angle signal. The core 68 is formedby a ring 70 of non-magnetic material, for example, aluminium and ofsubstantially rectangular cross-section. A strip 72 of ferromagneticmaterial is inserted as an armature into the ring 70 on the insidethereof. The rotor 14 comprises the circumferential portion 46 which isrotationally movable closely within the coil 66 and a strip 74 offerromagnetic material is inserted in the circumferential portion 46into a part of the circumference of the outer surface facing the coil66. The rotor 14 is arranged in the housing 10 for rotation through anangle exceeding 360°. There are thus not provided any stops which maygive reason to damage or maladjustment of the angle transmitter.

The associated circuit is illustrated in FIG. 3 and corresponds to thecircuit according to the German Patent Publication No. 3,212,149.

An oscillator 76 powered by a d.c. supply voltage at terminals 78,delivers an a.c. voltage at a transformer 80. This a.c. voltage producescurrents flowing through both halves of the coil 66. These currentsdepend upon the inductances of the two halves and thus upon the positionof the armature 72. The currents are rectified by related diodes 82 and84 and charge related capacitors 86 and 88. Associated ohmic resistors90 and 92 are connected parallel to the capacitors 86 and 88. Thecapicators 86 and 88 are connected with their voltages in opposition toeach other. When the inductances in the two halves of the coil 66 areequal, the capacitors 86 and 88 are symmetrically charged and theresulting d.c. voltage is zero. In the presence of an asymmetry, thecapacitor voltages also become asymmetric. There appears then aresulting d.c. voltage of either positive or negative sign dependingupon the direction of the angular deflection. This d.c. voltage issmoothed by means of a capacitor 94.

The d.c. voltage is applied to an input 98 of an operational amplifier100 via a resistor 96. At an other input 102 of the operationalamplifier 100 there is supplied via a resistor 104 a voltage tapped froma potentiometer 106.

The supply voltage for the potentiometer 106 is obtained via atransformer 108 which is powered by the oscillator 70, and a rectifierbridge 110. The rectified a.c. voltage is smoothed by means of acapacitor 112. The obtained d.c. voltage is stabilized by means of astabilizer circuit including a resistor 114 and a Zener diode 116.

A chain containing a resistor 118, a potentiometer 120 and a resistor122 is connected to the stabilized voltage. The slider of thepotentiometer 120 is connected with one side of the capacitor 94. Thereis thus provided a reference point for the voltages applied to theoperational amplifier. A chain containing three resistors 124, 126, 128is connected parallel to the chain 118, 120, 122. The potentiometer 106is connected to the central resistor 126.

A potentiometer 130 has a slider connected to the output of theoperational amplifier 100 and permits adjustment of the negativefeedback and thus of the gain. The output voltage is tapped betweenterminals 132 and 134.

I claim:
 1. Angle transmitter containing(a) a flat housing (10), (b) astator (12) arranged in the flat housing (10), (c) a rotor (14)rotatably supported relative to the stator (12) in the housing (10) andcooperating with the stator (12) in the housing (10) and cooperatingwith the stator (12) through a limited angular range for producing anoutput signal dependent upon the rotational angle, (d) an input shaft(16) and (e) a reducing gear (18) by means of which the input shaft (16)is coupled to the rotor (14),characterized in that (f) the input shaft(16) is journalled in said flat housing (10), (g) the rotor (14) isrotatably supported on the input shaft (16), the rotor comprising a hub(38) rotatably supported at the input shaft (16) adjacent the externaltoothing (22) of the input shaft (16) by means of two rolling bearings(40, 42), as well as an annular, disc-shaped central portion (44)adjoining the end of the hub (38) which is adjacent the externaltoothing (22), the rotor further including a circumferential portion(46) of basic cylindrical shape and which adjoins the central portion(44) along the circumference thereof on the side remote from the hub(38) and comprises the internal toothing, (h) the reducing gear (18) isarranged within the flat housing (10) in an annular space (20) formedbetween the rotor (14) and the input shaft (16), (i) the reducing gearcontaining an external toothing (22) at the input shaft (14) as well asan internal toothing (24) at the rotor (14) concentric relative to theinput shaft (16) and spaced therefrom and (j) in the housing (10),rotatably supported gear means (26) mesh with the external toothing (22)of the input shaft (16), on the one hand, and the internal toothing (24)of the rotor (14), on the other hand, the gear means protruding into theannular space (20) bounded by the circumferential portion (46), thecentral portion (44) and the input shaft (16).
 2. Angle transmitteraccording to claim 1, characterized in that the housing (10) is providedwith a magnetic shield (64) made of mu-metal.
 3. Angle transmitteraccording to claim 1, characterized in that(a) the gear means (26)comprise for play-free transmission of the rotational movement a firstand a second gear wheel (28, 30) similar thereto which are rotatablysupported at an axle (32) fixed relative to the housing andinterconnected by means of elastic members such that their teeth areslightly angularly offset from each other in an idle position (b) thefirst and the second gear wheel (28, 30) are in engagement with theexternal toothing (22) of the input shaft (16), (c) the gear means (26)further comprise a third gear wheel (34) which is also rotatablysupported on the axle (32) fixed relative to the housing, free of theexternal toothing (22) of the input shaft (16) and connected with theadjacent second gear wheel (30) by means of elastic members (36) suchthat their teeth are slightly angularly offset from each other in anidle position, and (d) the second and the third gear wheel (30, 34) arein engagement with the internal toothing (24) of the rotor (14). 4.Angle transmitter according to claim 1, characterized in that(a) thestator (12) comprises a coil (68) wound along a circular arc andcontaining a central tap and an at least partially ferromagnetic core(66), (b) the rotor (14) comprises an arcuately shaped, at leastpartially ferromagnetic armature externally extending around the coil(68) in a manner only affecting the stray field, and (c) a circuitarrangement is provided which responds to inductance changes of the coilportions formed on both sides of the central tap, for generating anangle signal.
 5. Angle transmitter according to claim 1, characterizedin that the input shaft (16) is journalled in rolling bearings (48, 50)provided in cover members (52, 54) of the housing (10), the hub (38) ofthe rotor (14) and the external toothing (22) of the input shaft (16)being arranged at the input shaft (16) between these rolling bearings(48, 50).
 6. Angle transmitter according to claim 5, characterized inthat signal processing electronic components are arranged in an annularspace (60) which is formed around the hub (38) between the centralportion (44) of the rotor (14) and the cover member (52) of the housing(10).
 7. Angle transmitter according to claim 4, characterized inthat(a) the core (66) is formed by a ring (70) which is made ofnon-magnetic material and has substantially rectangular cross-sectionand into which there is inserted on the inside a strip (72) offerromagnetic material, and (b) the rotor (14) comprises acircumferential portion (46) rotatably movable closely within the coil(68) and having an outer surface facing the coil and having insertedtherein in part of its circumference a strip (74) of ferromagneticmaterial.
 8. Angle transmitter according to claim 7, characterized inthat the rotor (14) is arranged in the housing (10) for rotation beyond360°.